The invention relates to methods for treatment of neurodegenerative disease and methods for delivery of therapeutic neurotrophins into the mammalian brain.
Neurotrophins play a physiological role in the development and regulation of neurons in mammals. In adults, basal forebrain cholinergic neurons, motor neurons and sensory neurons of the CNS retain responsiveness to neurotrophic factors and can regenerate after loss or damage in their presence. For this reason, neurotrophins are considered to have great promise as drugs for the treatment of neurodegenerative conditions such as Alzheimer""s Disease (AD), Parkinson""s Disease (PD), amyotrophic lateral sclerosis (ALS), peripheral sensory neuropathies and spinal cord injuries.
Clinical trials for the use of neurotrophins in the treatment of AD, ALS and sensory neuropathies are underway. However, the search for a protocol for delivery of neurotrophins to target tissues with minimal side effects (e.g., from diffusion to non-targeted cells or immune reaction to the delivery vehicle) and sufficient penetration of the CNS (e.g., bypassing the blood-brain barrier and achieving chronic delivery of neurotrophin to target cells) has not yet revealed a clear path for clinical administration of neurotrophins. In particular, effective delivery methods and dosing parameters have not yet been identified, although several methods have been proposed. Therefore, although the prospects for therapy of neurodegenerative disease of the brain and CNS are believed to be bright, a successful clinical protocol remains elusive.
The invention provides a clinically useful protocol for delivery of neurotrophins into the mammalian brain. The invention is particularly useful in treating neurodegenerative conditions in primates, in whom neurotrophins delivered according to the invention stimulate growth of neurons and recovery of neurological function.
More specifically, the invention consists of methods for intraparenchymal delivery of neurotrophins to defective, diseased or damaged cells in the mammalian brain. In one aspect, the invention provides a specific protocol for use in genetically modifying target cholinergic neurons (xe2x80x9ctarget cellsxe2x80x9d) to produce a therapeutic neurotrophin. The genetic modification of target cells is achieved by in vivo transfection of neurons targeted for treatment, or by transfection of cells neighboring these target neurons (neurons or glia), with a recombinant expression vector for expression of the desired neurotrophin in situ.
The location for delivery of individual unit dosages of neurotrophin into the brain is selected for proximity to previously identified defective, diseased or damaged target cells in the brain. To intensify exposure of such target cells to the endogenous growth factors, each delivery site is situated no more than about 500 xcexcm from a targeted cell and no more than about 10 mm from another delivery site. The total number of sites chosen for delivery of each unit dosage of neurotrophin will vary with the size of the region to be treated.
Optimally, for delivery of neurotrophin using a viral expression vector, each unit dosage of neurotrophin will comprise 2.5 to 25 xcexcl of an expression vector composition, wherein the composition includes a viral expression vector in a pharmaceutically acceptable fluid (xe2x80x9cneurotrophic compositionxe2x80x9d) and provides from 1010 up to 1015 NGF expressing viral particles per ml of neurotrophic composition. According to the method, neurotrophic composition is delivered to each delivery site in the brain by injection through a surgical incision, with delivery to be completed within about 5-10 minutes, depending on the volume of neurotrophic composition to be provided.
This targeted, regionally specific protocol for nervous system growth factor delivery avoids limitations imposed by diffusion of substances across the blood-brain barrier and through central nervous system (CNS) parenchyma, while avoiding potential adverse effects of neurotrophic factors delivered intact in a non-directed manner to the CNS.
The invention identifies and defines the required parameters of a method for successful regeneration of neurons in the brain with neurotrophins, especially the neurons whose loss is associated with neurodegenerative conditions with impairment of cognition such as AD.
The first method parameter defined by the invention is selection of a suitable target tissue. A region of the brain is selected for its retained responsiveness to neurotrophic factors. In humans, CNS neurons which retain responsiveness to neurotrophic factors into adulthood include the cholinergic basal forebrain neurons, the entorhinal cortical neurons, the thalamic neurons, the locus coeruleus neurons, the spinal sensory neurons and the spinal motor neurons. Abnormalities within the cholinergic compartment of this complex network of neurons have been implicated in a number of neurodegenerative disorders, including AD, Parkinson""s disease, and amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig""s disease). The cholinergic basal forebrain (particularly, the Ch4 region of the basal forebrain) is a particularly suitable target tissue.
Within the primate forebrain, magnocellular neurons Ch1-Ch4 provide cholinergic innervation to the cerebral cortex, thalamus and basolateral nucleus of the amygdala. In subjects with neurodegenerative diseases such as AD, neurons in the Ch4 region (nucleus basalis of Meynert) which have nerve growth factor (NGF) receptors undergo marked atrophy as compared to normal controls (see, e.g., Kobayashi, et al., Mol. Chem. Neuropathol., 15:193-206 (1991)).
In normal subjects, neurotrophins prevent sympathetic and sensory neuronal death during development and prevents cholinergic neuronal degeneration in adult rats and primates (Tuszynski, et al., Gene Therapy, 3:305-314 (1996)). The resulting loss of functioning neurons in this region of the basal forebrain is believed to be causatively linked to the cognitive decline experienced by subjects suffering from neurodegenerative conditions such as AD (Tuszynski, et al., supra and, Lehericy, et al., J. Comp. Neurol., 330:15-31 (1993)).
In human AD, basal forebrain neuronal loss occurs over an intraparenchymal area of approximately 1 cm in diameter. To treat affected neurons over such a large region, treatment with vector composition at upwards of 10 separate in vivo gene vector delivery sites is desirable. However, in treating localized injuries to the basal forebrain, the affected areas of the brain will likely be smaller such that selection of fewer delivery sites (e.g., 5 or fewer) will be sufficient for restoration of a clinically significant number of cholinergic neurons.
Importantly, specific in vivo gene delivery sites are selected so as to cluster in an area of neuronal loss. Such areas may be identified clinically using a number of known techniques, including magnetic resonance imaging (MRI) and biopsy. In humans, non-invasive, in vivo imaging methods such as MRI will be preferred. Once areas of neuronal loss are identified, delivery sites are selected for stereotaxic distribution so each unit dosage of NGF is delivered into the brain at, or within 500 xcexcm from, a targeted cell, and no more than about 10 mm from another delivery site.
A further parameter defined by the invention is the dosage of neurotrophin to be delivered into the target tissue. In this regard, xe2x80x9cunit dosagexe2x80x9d refers generally to the concentration of neurotrophin/ml of neurotrophic composition. For viral vectors, the neurotrophin concentration is defined by the number of viral particles/ml of neurotrophic composition. Optimally, for delivery of neurotrophin using a viral expression vector, each unit dosage of neurotrophin will comprise 2.5 to 25 xcexcl of a neurotrophic composition, wherein the composition includes a viral expression vector in a pharmaceutically acceptable fluid and provides from 1010 up to 1015 NGF expressing viral particles per ml of neurotrophic composition.
The neurotrophic composition is delivered to each delivery cell site in the target tissue by microinjection, infusion, scrape loading, electroporation or other means suitable to directly deliver the composition directly into the delivery site tissue through a surgical incision. The delivery is accomplished slowly, such as over a period of about 5-10 minutes (depending on the total volume of neurotrophic composition to be delivered).
Those of skill in the art will appreciate that the direct delivery method employed by the invention obviates a limiting risk factor associated with in vivo gene therapy; to wit, the potential for transfection of non-targeted cells with the vector carrying the NGF encoding transgene. In the invention, delivery is direct and the delivery sites are chosen so diffusion of secreted NGF takes place over a controlled and pre-determined region of the brain to optimize contact with targeted neurons, while minimizing contact with non-targeted cells.
Startlingly, in primates, a viral vector (AAV) with an operable neurotrophin encoding transgene has been shown to express human neurotrophin after delivery to the brain and to the CNS for up to 12 months. As such, the invention provides a chronically available source for neurotrophin in the brain.
Materials useful in the methods of the invention include in vivo compatible recombinant expression vectors, packaging cell lines, helper cell lines, synthetic in vivo gene therapy vectors, regulatable gene expression systems, encapsulation materials, pharmaceutically acceptable carriers and polynucleotides coding for nervous system growth factors of interest.
A. Neurotrophins
Known nervous system growth factors include nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4/5 (NT-4/5), neurotrophin-6 (NT-6), ciliary neurotrophic factor (CNTF), glial cell line-derived neurotrophic factor (GDNF), the fibroblast growth factor family (FGF""s 1-15), leukemia inhibitory factor (LIF), certain members of the insulin-like growth factor family (e.g., IGF-1), the neurturins, persephin, the bone morphogenic proteins (BMPs), the immunophilins, the transforming growth factor (TGF) family of growth factors, the neuregulins, epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and others. NGF and NT-3 in particular have been tested with promising results in clinical trials and animal studies (see, e.g., Hefti and Weiner, Ann Neurol., 20:275-281 (1986); Tuszynki and Gage, Ann. Neurol., 30:625-636 (1991); Tuszynski, et al., Gene Therapy, 3:305-314 (1996) and Blesch and Tuszynski, Clin. Neurosci., 3:268-274 (1996)). Of the known nervous system growth factors, NGF and NT-3 (for treatment of the Ch4 region, as in AD) are preferred for use in the invention.
Human (h) NGF and hNT3 are preferred for use in therapy of human disease according to the invention due to their relatively low immunogenicity as compared to allogenic growth factors. However, other nervous system growth factors are known which may also be suitable for use in the invention with adequate testing of the kind described herein.
Coding polynucleotides for hNGF and hNT3 are known, as are coding sequences for neurotrophins of other mammalian species (e.g., mouse, in which the coding sequence for NGF is highly homologous to the human coding sequence). For example, a cDNA including the coding sequence for hNGF is reported in GenBank at E03015 (Kazuo, et al., Japanese Patent Application No. JP19911175976-A, while the nucleotide sequence of genomic hNGF (with putative amino acid sequence) is reported in GenBank at HSBNGF (Ullrich, Nature, 303:821-825 (1983)) and the mRNA sequence is reported in GenBank at HSBNGFAC (Borsani, et al., Nucleic Acids Res., 18:4020 (1990)). The genomic nucleotide sequence of hNT3 is reported in GenBank at E07844 (Asae, et al., JP Patent Application No. 1993189770-A4). These references are incorporated herein to illustrate knowledge in the art concerning nucleotide and amino acid sequences for use in synthesis of neurotrophins.
B. Recombinant Expression Vectors
The strategy for transferring genes into target cells in vivo includes the following basic steps: (1) selection of an appropriate transgene or transgenes whose expression is correlated with CNS disease or dysfunction; (2) selection and development of suitable and efficient vectors for gene transfer; (3) demonstration that in vivo transduction of target cells and transgene expression occurs stably and efficiently; (4) demonstration that the in vivo gene therapy procedure causes no serious deleterious effects; and (5) demonstration of a desired phenotypic effect in the host animal.
Although other vectors may be used, preferred vectors for use in the methods of the present invention are viral and non-viral vectors. The vector selected should meet the following criteria: 1) the vector must be able to infect targeted cells and thus viral vectors having an appropriate host range must be selected; 2) the transferred gene should be capable of persisting and being expressed in a cell for an extended period of time (without causing cell death) for stable maintenance and expression in the cell; and 3) the vector should do little, if any, damage to target cells.
Because adult mammalian brain cells are non-dividing, the recombinant expression vector chosen must be able to transfect and be expressed in nondividing cells. At present, vectors known to have this capability include DNA viruses such as adenoviruses, adeno-associated virus (AAV), and certain RNA viruses such as HIV-based lentiviruses and feline immunodeficiency virus (FIV). Other vectors with this capability include herpes simplex virus (HSV).
For example, a HIV-based lentiviral vector has recently been developed which, like other retroviruses, can insert a transgene into the nucleus of host cells (enhancing the stability of expression) but, unlike other retroviruses, can make the insertion into the nucleus of non-dividing cells. This lentiviral vector has been shown to stably transfect brain cells after direct injection, and stably express a foreign transgene without detectable pathogenesis from viral proteins (see, Naldini, et al., Science, 272:263-267 (1996), the disclosure of which is incorporated by reference). Following the teachings of the researchers who first constructed the HIV-1 retroviral vector, those of ordinary skill in the art will be able to construct lentiviral vectors suitable for use in the methods of the invention (for more general reference concerning retrovirus construction, see, e.g., Kriegler, Gene Transfer and Expression, A Laboratory Manual, W. Freeman Co. (NY 1990) and Murray, EJ, ed., Methods in Molecular Biology, Vol. 7, Humana Press (NJ 1991)).
Adenoviruses and AAV have been shown to be quite safe for in vivo use and have been shown to result in long-term gene expression in vivo; they are therefore preferred choices for use in the methods of the invention, where safety and long-term expression of nervous system growth encoding transgenes (persisting for longer than necessary to stimulate regrowth of injured or diseased neurons) is necessary. Those of ordinary skill in the art are familiar with the techniques used to construct adenoviral and AAV vectors and can readily employ them to produce vector compositions useful in the claimed invention (for reference, see, e.g., Straus, The Adenovirus, Plenum Press (NY 1984), pp. 451-496; Rosenfeld, et al., Science, 252:431-434 (1991); U.S. Pat. No. 5,707,618 [adenovirus vectors for use in gene therapy]; and U.S. Pat. No. 5,637,456 [method for determining the amount of functionally active adenovirus in a vector stock], the contents of each of which is incorporated herein to illustrate the level of skill in the art).
Lentiviral-based vectors such as HIV and FIV are currently at earlier stages of development but also are attractive candidates for in vivo gene therapy based upon stability of expression in vivo and safety profiles.
Herpesviruses, alpha viruses and pox viruses are also well-characterized virus vectors which may be applied to the methods of the invention. Of these vectors, adeno-associated vectors are an especially attractive choice for their lack of pathogenicity and ability to insert a transgene into a host genome.
Non-viral delivery methods are also an option for use in the methods of the invention. In particular, the plasmid (in a xe2x80x9cnakedxe2x80x9d or lipid-complexed form), lipoplexes (liposome complexed nucleic acids), amino acid polymer complexes with nucleic acids and artificial chromosomes are all non-viral gene delivery agents which are demonstrably able to transduce cells and deliver a foreign transgene. Synthetic in vivo gene therapy vectors are also an option for use in the methods of the invention.
Construction of vectors for recombinant expression of nervous system growth factors for use in the invention may be accomplished using conventional techniques which do not require detailed explanation to one of ordinary skill in the art. For review, however, those of ordinary skill may wish to consult Maniatis et al., in Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, (NY 1982).
Briefly, construction of recombinant expression vectors employs standard ligation techniques. For analysis to confirm correct sequences in vectors constructed, the ligation mixtures may be used to transform a host cell and successful transformants selected by antibiotic resistance where appropriate. Vectors from the transformants are prepared, analyzed by restriction and/or sequenced by, for example, the method of Messing, et al., (Nucleic Acids Res., 9:309, 1981), the method of Maxam, et al., (Methods in Enzymology, 65:499, 1980), or other suitable methods which will be known to those skilled in the art. Size separation of cleaved fragments is performed using conventional gel electrophoresis as described, for example, by Maniatis, et al., (Molecular Cloning, pp. 133-134, 1982).
Expression of a gene is controlled at the transcription, translation or post-translation levels. Transcription initiation is an early and critical event in gene expression. This depends on the promoter and enhancer sequences and is influenced by specific cellular factors that interact with these sequences. The transcriptional unit of many prokaryotic genes consists of the promoter and in some cases enhancer or regulator elements (Banerji et al., Cell 27:299 (1981); Corden et al., Science 209:1406 (1980); and Breathnach and Chambon, Ann. Rev. Biochem. 50:349 (1981)). For retroviruses, control elements involved in the replication of the retroviral genome reside in the long terminal repeat (LTR) (Weiss et al., eds., The molecular biology of tumor viruses: RNA tumor viruses, Cold Spring Harbor Laboratory, (NY 1982)). Moloney murine leukemia virus (MLV) and Rous sarcoma virus (RSV) LTRs contain promoter and enhancer sequences (Jolly et al., Nucleic Acids Res. 11:1855 (1983); Capecchi et al., In: Enhancer and eukaryotic gene expression, Gulzman and Shenk, eds., pp. 101-102, Cold Spring Harbor Laboratories (NY 1991). Other potent promoters include those derived from cytomegalovirus (CMV) and other wild-type viral promoters.
Promoter and enhancer regions of a number of non-viral promoters have also been described (Schmidt et al., Nature 314:285 (1985); Rossi and de Crombrugghe, Proc. Natl. Acad. Sci. USA 84:5590-5594 (1987)). Methods for maintaining and increasing expression of transgenes in quiescent cells include the use of promoters including collagen type I (1 and 2) (Prockop and Kivirikko, N. Eng. J. Med. 311:376 (1984); Smith and Niles, Biochem. 19:1820 (1980); de Wet et al., J. Biol. Chem., 258:14385 (1983)), SV40 and LTR promoters.
In addition to using viral and non-viral promoters to drive transgene expression, an enhancer sequence may be used to increase the level of transgene expression. Enhancers can increase the transcriptional activity not only of their native gene but also of some foreign genes (Armelor, Proc. Natl. Acad. Sci. USA 70:2702 (1973)). For example, in the present invention collagen enhancer sequences are used with the collagen promoter 2(I) to increase transgene expression. In addition, the enhancer element found in SV40 viruses may be used to increase transgene expression. This enhancer sequence consists of a 72 base pair repeat as described by Gruss et al., Proc. Natl. Acad. Sci. USA 78: 943 (1981); Benoist and Chambon, Nature 290:304 (1981), and Fromm and Berg, J. Mol. Appl. Genetics, 1:457 (1982), all of which are incorporated by reference herein. This repeat sequence can increase the transcription of many different viral and cellular genes when it is present in series with various promoters (Moreau et al., Nucleic Acids Res. 9:6047 (1981).
Transgene expression may also be increased for long term stable expression using cytokines to modulate promoter activity. Several cytokines have been reported to modulate the expression of transgene from collagen 2(I) and LTR promoters (Chua et al., connective Tissue Res., 25:161-170 (1990); Elias et al., Annals N.Y. Acad. Sci., 580:233-244 (1990)); Seliger et al., J. Immunol. 141:2138-2144 (1988) and Seliger et al., J. Virology 62:619-621 (1988)). For example, transforming growth factor (TGF), interleukin (IL)-1, and interferon (INF) down regulate the expression of transgenes driven by various promoters such as LTR. Tumor necrosis factor (TNF) and TGF1 up regulate, and may be used to control, expression of transgenes driven by a promoter. Other cytokines that may prove useful include basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF).
Collagen promoter with the collagen enhancer sequence (Coll(E)) can also be used to increase transgene expression by suppressing further any immune response to the vector which may be generated in a treated brain notwithstanding its immune-protected status. In addition, anti-inflammatory agents including steroids, for example dexamethasone, may be administered to the treated host immediately after vector composition delivery and continued, preferably, until any cytokine-mediated inflammatory response subsides. An immunosuppression agent such as cyclosporin may also be administered to reduce the production of interferons, which downregulates LTR promoter and Coll(E) promoter-enhancer, and reduces transgene expression.
C. Pharmaceutical Preparations
To form a neurotrophic composition for use in the invention, neurotrophin encoding expression vectors (including, without limitation, viral and non-viral vectors) may be placed into a pharmaceutically acceptable suspension, solution or emulsion. Suitable mediums include saline and liposomal preparations.
More specifically, pharmaceutically acceptable carriers may include sterile aqueous of non-aqueous solutions, suspensions, and emulsions. Examples of non-aqueous solvents are propylene glycol, polyethylene glycol, vegetable oils such as olive oil, and injectable organic esters such as ethyl oleate. Aqueous carriers include water, alcoholic/aqueous solutions, emulsions or suspensions, including saline and buffered media. Parenteral vehicles include sodium chloride solution, Ringer""s dextrose, dextrose and sodium chloride, lactated Ringer""s or fixed oils. Intravenous vehicles include fluid and nutrient replenishers, electrolyte replenishers (such as those based on Ringer""s dextrose), and the like.
Preservatives and other additives may also be present such as, for example, antimicrobials, antioxidants, chelating agents, and inert gases and the like. Further, a composition of neurotrophin transgenes may be lyophilized using means well known in the art, for subsequent reconstitution and use according to the invention.
A colloidal dispersion system may also be used for targeted gene delivery. Colloidal dispersion systems include macromolecule complexes, nanocapsules, microspheres, beads, and lipid-based systems including oil-in-water emulsions, micelles, mixed micelles, and liposomes. Liposomes are artificial membrane vesicles which are useful as delivery vehicles in vitro and in vivo. It has been shown that large unilamellar vesicles (LUV), which range in size from 0.2-4.0 xcexcm can encapsulate a substantial percentage of an aqueous buffer containing large macro molecules. RNA, DNA and intact virions can be encapsulated within the aqueous interior and be delivered to cells in a biologically active form (Fraley, et al., Trends Biochem. Sci., 6:77, 1981). In addition to mammalian cells, liposomes have been used for delivery of operatively encoding transgenes in plant, yeast and bacterial cells. In order for a liposome to be an efficient gene transfer vehicle, the following characteristics should be present: (1) encapsulation of the genes encoding the antisense polynucleotides at high efficiency while not compromising their biological activity; (2) preferential and substantial binding to a target cell in comparison to non-target cells; (3) delivery of the aqueous contents of the vesicle to the target cell cytoplasm at high efficiency; and (4) accurate and effective expression of genetic information (Mannino, et al., Biotechniques, 6:682, 1988).
The composition of the liposome is usually a combination of phospholipids, particularly high-phase-transition-temperature phospholipids, usually in combination with steroids, especially cholesterol. Other phospholipids or other lipids may also be used. The physical characteristics of liposomes depend on pH, ionic strength, and the presence of divalent cations.
Examples of lipids useful in liposome production include phosphatidyl compounds, such as phosphatidylglycerol, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, sphingolipids, cerebrosides, and gangliosides. Particularly useful are diacylphosphatidylglycerols, where the lipid moiety contains from 14-18 carbon atoms, particularly from 16-18 carbon atoms, and is saturated. Illustrative phospholipids include egg phosphatidylcholine, dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine.
The targeting of liposomes can be classified based on anatomical and mechanistic factors. Anatomical classification is based on the level of selectivity, for example, organ-specific, cell-specific, and organelle-specific. Mechanistic targeting can be distinguished based upon whether it is passive or active. Passive targeting utilizes the natural tendency of liposomes to distribute to cells of the reticulo-endothelial system (RES) in organs which contain sinusoidal capillaries. Active targeting, on the other hand, involves alteration of the liposome by coupling the liposome to a specific ligand such as a monoclonal antibody, sugar, glycolipid, or protein, or by changing the composition or size of the liposome in order to achieve targeting to organs and cell types other than the naturally occurring sites of localization.
The surface of the targeted gene delivery system may be modified in a variety of ways. In the case of a liposomal targeted delivery system, lipid groups can be incorporated into the lipid bilayer of the liposome in order to maintain the targeting ligand in stable association with the liposomal bilayer. Various linking groups can be used for joining the lipid chains to the targeting ligand.
Following the protocol defined by the invention, direct delivery of a neurotrophic composition may be achieved by means familiar to those of skill in the art, including microinjection through a surgical incision (see, e.g., Capecchi, Cell, 22:479-488 (1980)); electropotation (see, e.g., Andreason and Evans, Biotechniques, 6:650-660 (1988)); infusion, chemical complexation with a targeting molecule or co-precipitant (e.g., liposome, calcium), and microparticle bombardment of the target tissue (Tang, et al., Nature, 356:152-154 (1992)).
In non-human primate subjects (Example III), the process of aging simulates the neurological changes in the brain experienced in aging humans. An non-aged animal model that also mimics loss of cholinergic neurons in, for example, AD, is transection of the fornix pathway connecting the septum from the hippocampus, which causes spontaneous degeneration of the same neurons which degenerate through aging (see, e.g., Example II). In rats and primates, such transections cause retrograde degeneration of cholinergic and non-cholinergic cell bodies in the septal nucleus and nucleus basalis (Ch4 region) of the brain.
These animals are tractable to treatment with neurotrophins, and model clinical responsiveness to such treatment comparable to aged humans (especially the non-human primates, whose brains are most similar in size and structure to humans). Data demonstrating the use and efficacy of the methods of the invention in these animal models are provided in the Examples.
Clinical evaluation and monitoring of treatment can be performed using the in vivo imaging techniques described above as well as through biopsy and histological analysis of treated tissue. In the latter respect, basal forebrain cholinergic neuronal numbers can be quantified in a tissue sample using, for example, anti-neurotrophin antibody (for immunoassay of secreted neurotrophin) or NGF-receptor (p75) and choline acetyltransferase (ChAT) for labeling of neurons. A sample protocol for in vitro histological analysis of treated and control tissue samples is described in the Examples.
The invention having been fully described, examples illustrating its practice are set forth below. These examples should not, however, be considered to limit the scope of the invention, which is defined by the appended claims. Those of ordinary skill in the art will appreciate that while the Examples illustrate an ex vivo application of the invention, the results achieved will be accessible through in vivo delivery of the nervous system growth factor encoding transgenes described, as taught herein, with in vivo gene delivery sites and direct delivery means substituted for the grafting sites and grafting methods discussed in the Examples.